Rugged target-analyte permeation testing instrument employing a consolidating block manifold

ABSTRACT

A target-analyte permeation testing instrument ( 10 ) characterized by a block manifold ( 100 ) retaining the testing cells ( 70   n ) of the instrument ( 10 ).

BACKGROUND

Permeation instruments are used to measure the transmission rate of a target analyte, such as oxygen, carbon dioxide or water vapor, through various samples, such as membranes, films, envelopes, bottles, packages, containers, etc. (hereinafter collectively referenced as “test films” for convenience). Typical test films are polymeric packaging films such as those constructed from low density polyethylene (LDPE), high density polyethylene (HDPE), oriented polypropylene (OPP), polyethylene terepthalate (PET), polyvinylidene chrloride (PVTDC), etc. Typically, the film to be tested is positioned within a test chamber to sealing separate the chamber into first and second chambers. The first chamber (commonly referenced as the driving or analyte chamber) is filled with a gas containing a known concentration of the target analyte (commonly referenced as a driving gas). The second chamber (commonly referenced as the sensing chamber) is flushed with an inert gas (commonly referenced as a carrier gas) to remove any target analyte from the cell. A sensor for the target analyte is placed in fluid communication with the sensing chamber for detecting the presence of target analyte that has migrated into the sensing chamber from the driving chamber through the test film. Exemplary permeation instruments for measuring the transmission rate of oxygen (O₂), carbon dioxide (CO₂) and water vapor (H₂O) through test films are commercially available from Mocon, Inc. of Minneapolis, Minn. under the designations OXTRAN, PERMATRAN-C and PERMATRAN-W, respectively.

Permeation instruments are being used more often to measure ever decreasing concentrations of target-analyte, into the ppm or even ppb range, and are therefore extremely sensitive to even minute atmospheric contamination of the fluids used in the instrument. Permeation instruments employ an extensive network of fluid interconnections with numerous valves to achieve the desired choreographed flow of driving and carrier gas through the instrument, especially when the instrument employs a plurality of testing cells in fluid communication with a single common target-analyte sensor. Each fitting in the fluid transfer system of the instrument is a potential source of contamination as atmospheric oxygen, carbon dioxide and water vapor leak around or permeate through the seals on the fittings, especially as the seals on the fittings loosen over time.

Accordingly, a substantial need exists for a permeation instrument capable near elimination of atmospheric-induced contamination of the driving and carrier gases flowing through the instrument throughout the lifespan of the instrument.

SUMMARY OF THE INVENTION

The invention is a target-analyte permeation testing instrument characterized by a block manifold. The instrument has a target-analyte sensor and a plurality of test cells for measuring target-analyte permeation rate of a test film. Each test cell defines a testing chamber and is operable for retaining a test film to sealingly divide the testing chamber into a driving chamber and a sensing chamber. The block manifold is fixed to the plurality of cells and has a plurality of channels in fluid communication with the testing chamber of each cell, a pressurized source of driving gas, a pressurized source of inert gas, and a target-analyte sensor. The plurality of channels are configured and arranged to selectively carry driving gas from the pressurized source of driving gas to the driving chamber of each cell, carry driving gas from the driving chamber of each cell to a driving gas exit port in the manifold, selectively carry inert gas from the pressurized source of inert gas to the sensing chamber of each cell, and selectively carry inert gas from the sensing chamber of each cell to the target-analyte sensor.

The block manifold can include a refillable first water reservoir in selective fluid communication with the source of driving gas and in fluid communication with the driving chamber of each cell, and a second refillable water reservoir in selective fluid communication with the source of inert gas and in fluid communication with the sensing chamber of each cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plumbing diagram of one embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Nomenclature Table 10 Target-Analyte Permeation Testing Instrument 20A Test Gas RH Control Valve 20B Carrier Gas RH Control Valve 30B_(wet) Catalyst Chamber in Wet Carrier Gas Line 30B_(dry) Catalyst Chamber in Dry Carrier Gas Line 40A_(wet) Particle Filter in Wet Test Gas Line 40A_(dry) Particle Filter in Dry Test Gas Line 40B_(wet) Particle Filter in Wet Carrier Gas Line 40B_(dry) Particle Filter in Dry Carrier Gas Line 50A Water Reservoir for Test Gas 50B Water Reservoir for Carrier Gas 60_(n) Capillary Restrictors 60₁A Capillary Restrictor for Test Gas Channel to First Test Cell 60₂A Capillary Restrictor for Test Gas Channel to Second Test Cell 60₁B Capillary Restrictor for Carrier Gas Channel to First Test Cell 60₂B Capillary Restrictor for Carrier Gas Channel to Second Test Cell 60₉B Capillary Restrictor for Carrier Gas Channel to Rezero Valve 70_(n) Testing Cells 70_(n)A Driving Chamber of Test Cell n 70_(n)B Sensing Chamber of Test Cell n 70_(n)Ax Exhaust from Driving Chamber of Test Cell n 70₁ First Testing Cells 70₁A Driving Chamber of First Test Cell 70₁Ax Exhaust from Driving Chamber of First Test Cell 70₁B Sensing Chamber of First Test Cell 70₂ Second Testing Cells 70₂A Driving Chamber of Second Test Cell 70₂Ax Exhaust from Driving Chamber of Second Test Cell 70₂B Sensing Chamber of Second Test Cell 80_(n)B Carrier Gas Sensing Chamber Exit Valve for Testing Cell n 80₁B First Test Cell Carrier Gas Exit Valve 80₁Bx Exhaust from Sensing Chamber of First Test Cell 80₂B Second Test Cell Carrier Gas Exit Valve 80₂Bx Exhaust from Sensing Chamber of Second Test Cell 88B Cell Selector Channel Conditioning Valve 88Bx Exhaust from Cell Selector Channel Conditioning Valve 89B Rezero Valve 89Bx Exhaust from Rezero Valve 100 Block Manifold 101A_(wet) Test Gas Water Reservoir Inlet Port 101A_(dry) Test Gas Water Reservoir Bypass Inlet Port 101B_(wet) Carrier Gas Water Reservoir Inlet Port 101B_(dry) Carrier Gas Water Reservoir Bypass Inlet Port 102 Carrier Gas Outlet Port to Sensor 200 Target-Analyte Sensor 210 Sensor Exhaust Valve 300_(n) Gas Flow Line n 300₀A_(wet) Test Gas Water Reservoir Inlet Line 300₀A_(dry) Test Gas Water Reservoir Bypass Inlet Line 300₀B_(wet) Carrier Gas Water Reservoir Inlet Line 300₀B_(dry) Carrier Gas Water Reservoir Bypass Inlet Line 300₁A_(in) Test Gas First Testing Cell Inlet Line 300₁B_(in) Carrier Gas First Testing Cell Inlet Line 300₂A_(in) Test Gas Second Testing Cell Inlet Line 300₂B_(in) Carrier Gas Second Testing Cell Inlet Line 300_(n)B_(out) Carrier Gas Outlet Line for Testing Cell n 300₁B_(out) Carrier Gas First Testing Cell Outlet Line 300₂B_(out) Carrier Gas Second Testing Cell Outlet Line 300₅ Shared Carrier Gas Testing Cell Outlet Line 300₉B Carrier Gas Rezero Line A Driving or Test Gas Source B Inert or Carrier Gas Source F Test Film

DESCRIPTION

Referring generally to FIG. 1, the invention is a target-analyte permeation testing instrument 10 characterized by a block manifold 100, preferably a solid block cast metal manifold 100 into which the appropriate channels and compartments are formed. The instrument 10 has a target-analyte sensor 200 and a plurality of test cells 70 _(n) for measuring target-analyte permeation rate of test films F_(n). Each test cell 70 _(n) defines a testing chamber and is operable for retaining a test film F to sealingly divide the testing chamber into a driving chamber 70 _(n)A and a sensing chamber 70 _(n)B. The cells 70 _(n) are secured to the block manifold 100. The block manifold 100 has a plurality of channels 300 _(n) in fluid communication with the testing chamber of each cell 70 _(n), a pressurized source of driving gas A, a pressurized source of inert gas B, and a target-analyte sensor 200. The plurality of channels 300 _(n) are configured and arranged to selectively carry driving gas from the pressurized source of driving gas A to the driving chamber 70 _(n)A of each cell 70 _(n), carry driving gas from the driving chamber 70 _(n)A of each cell 70 _(n) to a driving gas exit port 70 _(n)Ax in the manifold 100, selectively carry inert gas from the pressurized source of inert gas B to the sensing chamber 70 _(n)B of each cell 70 _(n), and selectively carry inert gas from the sensing chamber 70 _(n)B of each cell 70 _(n) to a the target-analyte sensor 200.

The block manifold 100 can include a refillable first water reservoir 50A in selective fluid communication with the source of driving gas A and in fluid communication with the driving chamber 70 _(n)A of each cell 70 _(n), and a second refillable water reservoir 50B in selective fluid communication with the source of inert gas B and in fluid communication with the sensing chamber 70 _(n)B of each cell 70 _(n).

An exemplary two-cell embodiment of the invention 10 is depicted in FIG. 1. The permeation testing instrument 10 preferably includes humidification systems for each of the test gas and carrier gas, such as described in U.S. Pat. Nos. 7,578,208 and 7,908,936, the disclosures of which are hereby incorporated by reference.

A source of dry test gas A fluidly communicates with a first humidification system that includes a wet line 300 ₀A_(wet) in fluid communication with a water reservoir 50A and a dry line 300 ₀A_(dry) that bypasses the water reservoir 50A. A test gas RH control valve 20A controls flow of test gas through the wet line 300 ₀A_(wet) and dry line 300 ₀A_(dry) according to a duty cycle for achieving the desired humidification level of the test gas.

The test gas wet line 300 ₀A_(wet) enters the block manifold 100 at inlet port 101A_(wet). The test gas dry line 300 ₀A_(dry) enters the block manifold 100 at inlet port 101A_(dry).

Upon exiting the water reservoir 50A, humidified test gas in the wet line 300 ₀A_(wet) is combined with dry test gas in the dry line 300 ₀A_(dry) and the combined test gas directed by test gas inlet lines 300 ₁A and 300 ₂A to the driving chambers 70 ₁A and 70 ₂A in the first testing cell 70 ₁ and second testing cell 70 ₂ respectively. Test gas flows through and exits each of the driving chambers 70 ₁A and 70 ₂A through an outlet port (unnumbered) and is vented from the block manifold at vent ports 70 ₁Ax and 70 ₂Ax respectively.

Particle filters 40A_(wet) and 40A_(dry) are preferably provided in the test gas wet line 300 ₀A_(wet) and test gas dry line 300 ₀A_(dry) respectively, for removing any entrained particulate matter from the test gas before it enters the block manifold 100.

In a similar fashion, a source of dry carrier gas B fluidly communicates with a second humidification system that includes a wet line 300 ₀B_(wet) in fluid communication with a water reservoir 50B and a dry line 300 ₀B_(dry) that bypasses the water reservoir 50B. A carrier gas RH control valve 20B controls flow of carrier gas through the wet line 300 ₀B_(wet) and dry line 300 ₀B_(dry) according to a duty cycle for achieving the desired humidification level of the carrier gas.

The carrier gas wet line 300 ₀B_(wet) enters the block manifold 100 at inlet port 101B_(wet). The carrier gas dry line 300 ₀B_(dry) enters the block manifold 100 at inlet port 101B_(dry).

Upon exiting the water reservoir 50B, humidified carrier gas in the wet line 300 ₀B_(wet) is combined with dry carrier gas in the dry line 300 ₀B_(dry) and the combined carrier gas directed by carrier gas inlet lines 300 ₁B and 300 ₂B to the sensing chambers 70 ₁B and 70 ₂B in the first testing cell 70 ₁ and second testing cell 70 ₂ respectively. Carrier gas flows through and exits each of the sensing chambers 70 ₁B and 70 ₂B through an outlet port (unnumbered) and is directed by dedicated outlet channels 300 ₁B_(out) and 300 ₂B_(out) respectively, to a common channel 300 ₅ in fluid communication with a target-analyte sensor 200 located external to the block manifold 100.

Common channel 300 ₅ exits the block manifold 100 at outlet port 102.

Particle filters 40B_(wet) and 40B_(dry) are preferably provided in the carrier gas wet line 300 ₀B_(wet) and carrier gas dry line 300 ₀B_(dry) respectively, for removing any entrained particulate matter from the carrier gas before it enters the block manifold 100.

Target-analyte catalytic converters 30B_(wet) and 30B_(dry) are preferably provided in the carrier gas wet line 300 ₀B_(wet) and carrier gas dry line 300 ₀B_(dry) respectively, for converting any target-analyte in the carrier gas (e.g., O₂) to a molecular species (e.g., H₂O when the target analyte is O₂) that will not be detected by the target-analyte sensor 200.

Capillary restrictors 60 ₁A, 60 ₂A, 60 ₁B and 60 ₂B are preferably provided in the test gas inlet lines 300 ₁A and 300 ₂A, and carrier gas inlet lines 300 ₁B and 300 ₂B respectively, for facilitating a consistent and equal flow of gas into the driving chambers 70 ₁A and 70 ₂A of the testing cells 70 ₁ and 70 ₂, and the sensing chambers 70 ₁B and 70 ₂B of the testing cells 70 ₁ and 70 ₂ respectively. The capillary restrictors 60 _(n) are preferably side mounted onto the block manifold 100.

Valves 80 ₁B and 80 ₂B are provided in the dedicated outlet channels 300 ₁B_(out) and 300 ₂B_(out) respectively, for selectively and mutually exclusively allowing passage of carrier gas, containing any target-analyte that has permeated through the test film F, from each of the sensing chambers 70 ₁B and 70 ₂B into sensing engagement with the sensor 200. When closed, the valves 80 ₁B and 80 ₂B vent carrier gas, containing any target-analyte that has permeated through the test film F, to atmosphere through vent ports 80 ₁Bx and 80 ₂Bx in the manifold 100. The valves 80 _(n)B are preferably side mounted onto the block manifold 100.

The instrument 10 depicted in FIG. 1 includes an optional channel conditioning feature. Permeation testing instruments 10 employ a very low mass flow through rate through the gas flow lines 300 n of the instrument 10 to limit the creation of any pressure differentials in the instrument 10 that could impact humidification of the test and/or carrier gases or create a pressure-induced driving force across a test film F. This low mass flow rate through the instrument 10 imposes a significant time delay between measurements from different testing cells 70 _(n) as both the “stale” carrier gas contained in the length of the testing cell outlet line 300 _(n)B_(out) for the upcoming testing cell 70 _(n) to be measured and the “inapplicable” carrier gas contained in the length of the shared outlet line 300 ₅ from the previously measured testing cell 70 _(n) is flushed from the lines and replaced with fresh carrier gas, containing any target-analyte that has permeated through the test film F, from the upcoming testing cell 70 _(n). A channel conditioning feature employs a cell selector channel conditioning valve 88B in the shared outlet line 300 ₅ for allowing, in coordination with opening and closing of valves 80 _(n)B for the upcoming and previous testing cells 70 _(n), for advanced venting of “stale” carrier gas contained in the length of the outlet line 300 _(n)B_(out) for the upcoming testing cell 70 _(n). The cell selector channel conditioning valve 88B is operable as between a flow-through state, in which carrier gas is directed to the sensor 200, and a vent state, in which carrier gas is vented to atmosphere through a vent port 88Bx in the block manifold 100. The cell selector channel conditioning valve 88B is preferably side mounted to the block manifold 100.

The instrument 10 depicted in FIG. 1 includes an optional rezero feature. Rezero is a method of measuring residual target-analyte contained in the carrier gas during performance of testing that includes the steps of bypassing the test cell(s) 70 _(n) and directly measuring the carrier gas target-analyte level, which is then subtracted from the measured transmission rate of the target-analyte level for each sample.

The rezero feature includes a rezero line 300 ₉B upstream from the testing cells 70 _(n) for bypassing the testing cells 70 _(n) and carrying carrier gas directly to the sensor 200. A rezero valve 89B is provided in the rezero line 300 ₉B for selectively directing carrier gas to the sensor 200 or venting carrier gas from the block manifold 100 at vent port 89Bx. The rezero valve 89B is preferably side mounted to the block manifold 100.

A capillary restrictor 60 ₉B is preferably provided in the carrier gas rezero line 300 ₉B for facilitating a consistent and equal flow of carrier gas into the sensing chambers 70 ₁B and 70 ₂B of the testing cells 70 ₁ and 70 ₂ respectively. The capillary restrictor 60 ₉B is, as with the other capillary restrictors, preferably side mounted onto the block manifold 100.

The sensor 200 is selected to measure the appropriate target-analyte (e.g., oxygen (O₂), carbon dioxide (CO₂) or water vapor (H₂O)). Selection of a suitable sensor 200 is well within the knowledge and expertise of a person having routine skill in the art. The sensor 200 is preferably a coulox sensor and is equipped with an exhaust valve 210 for preventing atmospheric contamination of the sensor when there is no flow of carrier gas to the sensor 200. 

I claim:
 1. A target-analyte permeation testing instrument for measuring target-analyte permeation rate of a test film in test cell, the instrument having a target-analyte sensor and a plurality of test cells each defining a testing chamber with each test cell operable for retaining a test film to sealingly divide the testing chamber into a driving chamber and a sensing chamber, the target-analyte permeation testing instrument characterized by a block manifold (-) fixed to the plurality of cells, and (-) having a plurality of channels in fluid communication with the testing chamber of each cell, a pressurized source of driving gas, a pressurized source of inert gas, and the target-analyte sensor, wherein the plurality of channels are configured and arranged to (i) selectively carry driving gas from the pressurized source of driving gas to the driving chamber of each cell, (ii) carry driving gas from the driving chamber of each cell to a driving gas exit port in the manifold, (iii) selectively carry inert gas from the pressurized source of inert gas to the sensing chamber of each cell, and (iv) selectively carry inert gas from the sensing chamber of each cell to the target-analyte sensor.
 2. The target-analyte permeation testing instrument of claim 1 wherein the block manifold further includes a refillable first water reservoir in selective fluid communication with the source of driving gas and in fluid communication with the driving chamber of each cell, and a second refillable water reservoir in selective fluid communication with the source of inert gas and in fluid communication with the sensing chamber of each cell.
 3. The target-analyte permeation testing instrument of claim 1 wherein the block manifold is constructed from a single unitary metal block.
 4. The target-analyte permeation testing instrument of claim 1 wherein the channels in fluid communication with the pressurized source of driving gas and the driving chamber of each cell are in fluid communication with at least one block mounted valve operable for effecting selective delivery of driving gas to the driving chambers of the cells.
 5. The target-analyte permeation testing instrument of claim 1 wherein the channels in fluid communication with the pressurized source of inert gas and the sensing chamber of each cell are in fluid communication with at least one block mounted valve operable for effecting selective delivery of inert gas to the sensing chambers of the cells.
 6. The target-analyte permeation testing instrument of claim 1 wherein the channels in fluid communication with the sensing chamber of each cell and the target-analyte sensor are in fluid communication with at least one block mounted valve operable for effecting selective delivery of inert gas from the sensing chambers of the cells to the target-analyte sensor. 